Makes power profiles handling available over D-Bus.

 power-profiles-daemon offers to modify system behaviour based upon
 user-selected power profiles. There are 3 different power profiles, a
 "balanced" default mode, a "power-saver" mode, as well as a "performance"
 mode. The first 2 of those are available on every system. The "performance"
 mode is only available on select systems and is implemented by different
 "drivers" based on the system or systems it targets.
 .
 In addition to those 2 or 3 modes (depending on the system),
 "actions" can be hooked up to change the behaviour of a particular device.
 For example, this can be used to disable the fast-charging for some USB
 devices when in power-saver mode.
 .
 Note that power-profiles-daemon does not save the currently active
 profile across system restarts and will always start with the "balanced"
 profile selected.